The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, gas regulators are implemented into these distribution systems to ensure that the delivered gas meets the requirements of the end-user facilities. Conventional gas regulators generally include a closed-loop control actuator for sensing and controlling the pressure of the delivered gas.
In addition to a closed loop control, some conventional gas regulators include a balanced trim to improve the reaction of the gas regulator to variations in the downstream pressure. The balanced trim is adapted to reduce the influence of the upstream pressure on the performance of the gas regulator. The upstream pressure is placed in fluid communication with a balancing diaphragm to apply a force to the control element of the gas regulator in the opposite direction as the force of the downstream pressure. Accordingly, as the upstream pressure varies, a corresponding force is applied to balance the force created by the upstream pressure as described further below so that the gas regulator acts in response to the downstream pressure only.
FIGS. 1 (closed position) and 2 (full open position) depict one conventional gas regulator 10. The regulator 10 generally comprises an actuator 12 and a regulator valve 14. The regulator valve 14 defines an inlet 16 for receiving gas from a gas distribution system, for example, and an outlet 18 for delivering gas to an end-user facility such as a factory, a restaurant, an apartment building, etc. having one or more appliances, for example. Additionally, the regulator valve 14 includes a valve port 20 disposed between the inlet 16 and the outlet 18. Gas must pass through the valve port 20 to travel between the inlet 16 and the outlet 18 of the regulator valve 14.
The actuator 12 is coupled to the regulator valve 14 to ensure that the pressure at the outlet 18 of the regulator valve 14, i.e., the outlet pressure, is in accordance with a desired outlet or control pressure, known as the setpoint pressure. The actuator 12 is therefore in fluid communication with the regulator valve 14 via a valve mouth 22 and an actuator mouth 24. The actuator 12 includes a control assembly 26 for sensing and regulating the outlet pressure of the regulator valve 14. Specifically, the control assembly 26 includes a diaphragm 28, a piston 30, and a control arm 32 having a valve disc 34 operatively connected thereto. The conventional balanced trim valve disc 34 includes a generally cylindrical body 36 and a sealing insert 38 fixed to the body 36. The control assembly 26 may also include a balanced trim assembly 40 with a balancing diaphragm 42 to offset the force applied to the valve disc 34 by the upstream pressure. The actuator diaphragm 28 senses the outlet pressure of the regulator valve 14 via a Pitot tube 44 placing the outlet 18 in fluid communication with the interior of the actuator 12 and a bottom-side of the actuator diaphragm 28. The control assembly 26 further includes a control spring 46 in engagement with a top-side of the diaphragm 28 to offset the sensed outlet pressure. Accordingly, the desired outlet pressure, which may also be referred to as the control pressure or the actuator setpoint pressure, is set by the selection of the control spring 46.
The diaphragm 28 is operably coupled to the control arm 32, and therefore, the valve disc 34 via the piston 30, controls the opening of the regulator valve 14 based on the sensed outlet pressure. For example, when an end user operates an appliance, such as a furnace, for example, that places a demand on the gas distribution system downstream of the regulator 10, the outlet flow increases, thereby decreasing the outlet pressure. Accordingly, the diaphragm 28 senses this decreased outlet pressure. This allows the control spring 46 to expand and move the piston 30 and the right-side of the control arm 32 downward, relative to the orientation of FIG. 1. This displacement of the control arm 32 moves the valve disc 34 away from the valve port 20 to open the regulator valve 14. FIGS. 2 and 3 depict the valve disc 34 in a normal, open operating position. So configured, the appliance may draw gas through the valve port 20 toward the outlet 18 of the regulator valve 14.
In the conventional regulator 10, the control spring 46 inherently generates less force as it expands towards an uncompressed length when displacing the control arm 32 to open the valve port 20. Additionally, as the control spring 46 expands, the diaphragm 28 deforms, which increases the area of the diaphragm 28. The decreased force supplied by the control spring 46 and the increased area of the diaphragm 28 in this operational scenario combine to create a regulator response wherein the force provided by the control spring 46 cannot adequately balance the force generated by the diaphragm 28 thereby resulting in an outlet control pressure that is less than that originally set by the user. This phenomenon is known as “droop.” When “droop” occurs, the outlet pressure decreases below its set control pressure and the regulator 10 may not function as intended.
In the conventional regulator 10 depicted in FIGS. 1-3, the control assembly 26 further functions as a relief valve, as mentioned above. Specifically, the control assembly 26 also includes a relief spring 48 and a release valve 50. The diaphragm 28 includes an opening 52 through a central portion thereof and the piston 30 includes a sealing cup 54. The relief spring 48 is disposed between the piston 30 and the diaphragm 28 to bias the diaphragm 28 against the sealing cup 54 to close the opening 52, during normal operation. Upon the occurrence of a failure such as a break in the control arm 32, the control assembly 26 is no longer in direct control of the valve disc 34 and inlet flow will move the valve disc 34 to an extreme open position. This allows a maximum amount of gas to flow into the actuator 12. Thus, as the gas fills the actuator 12, pressure builds against the diaphragm 28 forcing the diaphragm 28 away from the sealing cup 54, thereby exposing the opening 52. The gas therefore flows through the opening 52 in the diaphragm 28 and toward the release valve 50. The release valve 50 includes a valve plug 56 and a release spring 58 biasing the valve plug 56 into a closed position. Upon the pressure within the actuator 12 and adjacent the release valve 50 reaching a predetermined threshold pressure, the valve plug 56 displaces upward against the bias of the release spring 58 and opens, thereby exhausting gas into the atmosphere and reducing the pressure in the regulator 10.
In most implementations, it is preferable to sense the downstream pressure as shown in FIGS. 1-3 within the outlet 18. The Pitot tube 44 as positioned provides rapid feedback of the downstream pressure to the control assembly 26 and eliminates the need for an external downstream pressure feedback line. A regulator's performance is dictated by the volume of a fluid that can be transferred downstream while maintaining a designated outlet pressure. The smoother the fluid flow before the sense point of the Pitot tube 44, the more accurate the pressure sensed by the Pitot tube 44 and provided to the control assembly 26. In the regulator 10 as shown, however, the fluid passing through the valve port 20 is dispersed within the valve mouth 22 and outlet 18 such that the fluid experiences and maintains turbulent flow as it passes the sense point of the Pitot tube 44 under typical conditions. The turbulent flow leads to substandard sensing of the downstream fluid pressure.
Better regulation of the fluid flow and, correspondingly, the downstream pressure, may be achieved by using flow conditioning to artificially raise the amount of fluid volume transferred by a gas regulator. The flow conditioning quickly transitions the fluid from turbulent flow to laminar flow to provide for more accurate sensing of the downstream pressure. In one example of flow conditioning shown in FIGS. 4-6, a regulator 60 includes a regulator valve 62 having a modified outlet 64 configured to receive a flow control subassembly 66. The flow control subassembly 66 includes a screen 68 having a plurality of baffles 70, a semicircular sieve 72 with a plurality of holes 74 therethrough, and a central sensing tube 76. An inward end of the sensing tube 76 in placed in fluid communication with the interior of the actuator 12. The fluid flow is converted from turbulent flow to laminar flow as the fluid passes between the baffles 70 and through the holes 74, resulting in a more accurate measurement of the downstream pressure at the sense point of the sensing tube 76. While being effective at conditioning the flow, the subassembly 66 is relatively expensive to fabricate. Moreover, the subassembly 66 requires modifications to the standard regulator valve body and is not readily transitioned to other body sizes. Therefore, a need exists for flow conditioning in a gas regulator that is less expensive to implement and readily implemented in a variety of regulator valve sizes and body types.